1. Field of the Invention
There is increasing concern with the manner in which drugs are administered since both the manner and amount of the drug which is administered, affects the blood level of the drug during an extended period of time and in many instances, the effectiveness of the drug is directly related to the concentration of the drug in the bloodstream. The rate at which the desired blood level is achieved or exceeded will depend upon the nature of the drug, the manner of administration, the dosage, as well as the rate of metabolism. The rate at which a drug will enter the bloodstream when administered other than intravenously and the rate at which the drug is metabolized varies widely with individuals. Furthermore, the level of effectiveness will also vary widely with individuals.
It is therefore desirable when administering drugs to ascertain the individual's level of effectiveness, the rate at which this level is achieved at a particular dosage and the time for which the level is maintained. In this manner, the amount of drug which is administered can then be carefully monitored to maintain the desired level. In this way, effectiveness can be assured and side effects minimized.
In order to monitor a drug in a physiological fluid, it is necessary to have sensitive tests which enable the rapid determination of the drug as distinct from any ineffectual metabolites. Thus, the test must clearly distinguish between the drug of interest and compounds of very similar structure. In competitive protein binding assays, antibodies are employed which are prepared by means of antigenic conjugates of derivatives of the drug of interest. In order for the antibodies to be effective, they must be produced in high titer, have a strong binding constant to the drug of interest, and weakly bind to compounds of similar structure.
With many drugs, there may be closely analogous compounds which may be administered which have different activity or may be metabolized to other compounds of different activity. In these situations, it is necessary to distinguish between the compound which is administered and its metabolite, so that the individual concentrations of each of the drugs in the bloodstream can be determined and monitored.
There is also a need for a reagent which provides a measurable signal related to the amount of drug present in the assay medium. Where antibodies are involved, the reagent must effectively compete with the drug for antibody binding in a reproducible manner and provide for significant changes in the signal with small changes in the drug concentration over the concentration range of interest.
Other considerations for a reagent are that it is not affected by materials present in the unknown sample to be assayed or that materials which do interfere may be removed from the sample. Additionally, a reagent should provide an easily determinable signal, should be stable under the assay conditions, should have a good storage life and should be readily recognized by the antibodies for the drug.
2. Brief Description of the Prior Art
Descriptions of competitive protein binding assays may be found in U.S. Pat. Nos. 3,817,837, 3,850,752, 3,690,834, and in an article by Murphy, 27 J. Clin. Endocr. 973(1967). Preparation of antigenic conjugates and antibodies for a number of different drugs may be found in U.S. Pat. Nos. 3,888,866, 3,766,162, 3,843,696 and 3,878,178. U.S. Pat. No. 3,875,011 discloses glucose-6-phosphate dehydrogenase conjugates for use in homogeneous enzyme immunoassays.
Articles concerned with antibodies to procainamide and its derivative include Russell and Ziff, Clin. Exp. Immunol (1968) 3, 901 and Rous et al, Clin. Chem. (1977), 23, 705.